This invention relates to natural fats and natural fat blends and their use in providing oxidation-resistant shortenings as ingredients in producing baked, fried, and other prepared foods.
The discussion below is provided to assist the understanding of the reader. None of the information provided or references cited are admitted to be prior art to the present invention.
In providing shortenings for the production of commercially prepared foods such as baked and fried food products, much effort has been devoted to improving the oxidation-resistance of the shortening. The oxidation-resistance of a shortening is important for preventing or delaying the onset of rancidity in the fat component of the food, and extending the food's shelf-life.
There are several well known methods which are currently used for improving the oxidation resistance of shortenings. These include the partial hydrogenation of the triglyceride's fatty acids (resulting in a decreased proportion of the polyunsaturated linoleic and linolenic acids which are prone to oxidation), the addition of one or more antioxidants such as alpha-tocopherol or TBHQ to the shortening composition, and the interesterification and randomization of fatty acids in triglyceride mixtures constituting blends of fats and oils.
Most references in the literature describing the blending of saturated fats and polyunsaturated vegetable oils, link such blending with the interesterification or partial hydrogenation of fatty acids in these blends. It is well known in the art that interesterification allows the randomization of polyunsaturated fatty acids with saturated and monounsaturated fatty acids in the triglyceride structure. This randomization is used to alter important physical properties such as the hardness, plasticity, and melting point of fats.
With baking shortenings, control of these properties, may be used to provide firm fats for producing flaky pastry or oily shortenings for more compact pastry. Controlled hydrogenation, interesterification and blending of fats and oils is also important in producing frying oils which have sufficient resistance to high temperature oxidation (and thereby adequate frying lifetime), while also retaining a sufficiently low melting temperature (a sufficient proportion of unsaturated fatty acids) to avoid a fatty mouth feel. Saturated fats and hydrogenated oils with a relatively high melting point (significantly above body temperature) are associated with a fatty mouth feel. For example, the proportion of tripalmitin (mp=66.degree. C.) and other trisaturated triglycerides in undiluted palm oil produces a fatty mouth feel in foods fried in this oil. For this reason, and for nutritional reasons it is desirable to blend palm oil with a vegetable oil such as soybean oil to lower the melting temperature of the palm fat by increasing the proportion of polyunsaturated fatty acids in the blend. Fractionating the palm oil produces lower melting point fractions such as palm olein and palm superolein (double fractionated), but for the nutritional reasons described in U.S. Pat. No. 5,578,334, an increase in the polyunsaturated fatty acid content of the fat, i.e., shortening, is desirable.
There are references in the literature to the direct blending of polyunsaturated vegetable oils with more stable saturated fats to reduce the rate of oxidation of the vegetable oils. For example, Berry et al. (Palm Oil Prod. Technol. Eighties, Rep. Proc. Int. Conf. 1981, pp. 505-518) reported that the oxidative stability of soybean oil was improved by blending with palm olein. Similarly, Lim et al.(Yukagaku 1990, 39(12), 1045-1049) demonstrated that when soybean oil was blended with either crude palm oil, refined bleached and deodorized palm oil, or refined palm kernel oil, oxidative stability of the soybean oil increased. Kajimoto et al.(Nippon Eiyo, Shokuryo Gakkaishi 1991, 44(6), 499-505) showed that the oxidative stabilities of both soybean oil and canola (rapeseed) oil are enhanced by blending with palm oil. Similarly, Han et al., (Han'guk Sikp'um Kwahakhoechi 1991, 23(4), pp.465-470) showed that the thermal and oxidative stabilities of soybean oil are enhanced by blending with palm oil in which the ratio of palm oil to soybean oil is greater than 50%. In yet another study, Neff et al., (J. Am. Oil Chem. Soc. 71(10),1111-1116, 1994) compared resistance to autoxidation provided by either blending or interesterifying between 1 and 10 parts palm olein with 1 part soybean oil, and found blending more effective. Minal et al., (Palm Oil Dev. (21), 31-34, 1994)), describe the blending of palm oil with either sunflower oil or soybean oil to produce frying oils with improved stability.
Other reasons for blending palm fat with polyunsaturated vegetable oils are described in the prior art literature. Rasid et al., (Palm Oil Dev. (21), 24-27, 1994) show that a decrease is achieved in the cloud point of palm oil and palm olein-containing edible oils by blending the oils with polyunsaturated vegetable oils including canola, rice-bran, soybean, sunflower and cottonseed oils. Pala, (Malaysian Oil Sci. Technol. 4(1), 166-175, 1995) describe and compare the cold stability and frying performance of blends of either sunflower, soybean, or cottonseed oils with double fractionated palm olein (also known as palm superolein), and conclude that for frying, palm-soybean oil blends are superior. NorAini et al., (J. Am. Oil Chem. Soc. 72(4), 443-448, 1995) compare the cloud points of blends containing double fractionated palm olein and either canola (rapeseed) oil or soybean oil, and show that blends with canola oil are superior in achieving lower cloud points to remain liquid at lower temperature.
None of the above references, however, describe the blending of palm fat and corn oil to provide improved shortenings.